(i) Technical Field
A certain aspect of the embodiments discussed herein is related to a semiconductor device. Another aspect o the embodiments is related to a semiconductor device configured to have a field plate formed on an insulation film between a gate finger and a drain finger.
(ii) Related Art
Semiconductor devices using a nitride semiconductor are used as power devices that operate at high frequencies and output high power. FETs (Field Effect Transistors) such as a HEMT (High Electron Mobility Transistor) are known as transistors suitable for amplification in a high-frequency or RF (Radio Frequency) band, which may include microwaves, quasi-millimeter waves or millimeter waves.
In the power FET, it is known to use a field plate on an insulation film between a gate finger and a drain finger (see Japanese Patent Application Publication No. 2007-273920, for example). The field plate that is kept at a predetermined potential (for example, ground potential) functions to relax the electric field intensity under the field plate between the gate finger and the drain finger. The field plate provided above an area having a strong electric field intensity equalizes the electric field intensity between the gate finger and the drain finger, and improves the source-drain breakdown voltage or the gate-drain breakdown voltage. This enables high power amplification. The equalization of the electric field intensity suppresses the current collapse.
As illustrated in FIG. 2(a) of the above application publication, the insulation later provided so as to cover the gate electrode has a step resulting from the shape of the gate electrode, and the field plate is formed along the step of the insulation layer. The semiconductor device having this structure has a possibility of failure when it is operated with a high voltage at high temperature.